Occurrence and diversity of human enteric viruses in bivalve mollusks from the Amazon mangrove ecosystem in Brazil

Coastal mangroves are vital ecosystems located at the land-sea interface and, thus, highly vulnerable to anthropogenic contamination. Among their rich biodiversity, these areas host bivalve mollusks recognized as waterborne pathogen bioindicators. In this sense, this study aimed to assess the occurrence and genetic diversity of multiple human enteric viruses and the presence of the human fecal bioindicator crAssphage in bivalve mollusks from the Amazon Mangrove Region in Brazil, a shellfish harvesting and consumption hotspot. Oysters and mussels were sampled from three Maranhão Island municipalities, in the state of Maranhão, Northeastern Brazil, between August 2023 and July 2024. Eighty-nine samples were processed according to the ISO 15216-1:2017 standard. Viral screening was performed by the TaqMan real-time PCR assay, and molecular characterization by Sanger sequencing. Rotavirus group A and norovirus GII were the most prevalent enteric viruses (18%, each), followed by human mastadenovirus (14.6%), norovirus GI (6.7%), and hepatitis A virus (3.4%), while RVA showed the highest viral load (2.6 × 10⁶ gc/g). Detected genotypes included norovirus GII.8 and GI.5, RVA G3, P[8]-III, and I2, HAdV-F41, and HAV IA-III. Viral occurrence was higher during the rainy season, coinciding with increased runoff and sewage inputs. CrAssphage exhibited the highest detection frequency (38.2%) and showed significant positive associations with multiple enteric viruses. These findings represent the first report of multiple enteric viruses in bivalves from natural Amazon mangrove banks in Maranhão, highlighting a recognized food safety hazard associated with shellfish consumption.